Intravenously administered glucocorticoids , such as prednisone , are the standard of care in acute GvHD  and chronic GVHD.  The use of these glucocorticoids is designed to suppress the T-cell-mediated immune onslaught on the host tissues; however, in high doses, this immune-suppression raises the risk of infections and cancer relapse. Therefore, it is desirable to taper off the post-transplant high-level steroid doses to lower levels, at which point the appearance of mild GVHD may be welcome, especially in HLA mis-matched patients, as it is typically associated with a graft-versus-tumor effect. [ citation needed ] . Cyclosporine and tacrolimus are inhibitors of calcineurin. Both substances are structurally different but have the same mechanism of action. Cyclosporin binds to the cytosolic protein Peptidyl-prolyl cis-trans isomerase A (known as cyclophilin), while tacrolimus binds to the cytosolic protein Peptidyl-prolyl cis-trans isomerase FKBP12. These complexes inhibit calcineurin, block dephosphorylation of the transcription factor NFAT of activated T-cells and its translocation into the nucleus  . Standard prophylaxis involves the use of cyclosporine for six months with methotrexate. Cyclosporin levels should be maintained above 200 ng/ml  . Other substances that have been studied for GvHD prophylaxis include, for example: sirolism, pentostatin and alemtuzamab  .
Steroid isolation , depending on context, is the isolation of chemical matter required for chemical structure elucidation, derivitzation or degradation chemistry, biological testing, and other research needs (generally milligrams to grams, but often more  or the isolation of "analytical quantities" of the substance of interest (where the focus is on identifying and quantifying the substance (for example, in biological tissue or fluid). The amount isolated depends on the analytical method, but is generally less than one microgram.  [ page needed ] The methods of isolation to achieve the two scales of product are distinct, but include extraction , precipitation, adsorption , chromatography , and crystallization . In both cases, the isolated substance is purified to chemical homogeneity; combined separation and analytical methods, such as LC-MS , are chosen to be "orthogonal"—achieving their separations based on distinct modes of interaction between substance and isolating matrix—to detect a single species in the pure sample. Structure determination refers to the methods to determine the chemical structure of an isolated pure steroid, using an evolving array of chemical and physical methods which have included NMR and small-molecule crystallography .  :10–19 Methods of analysis overlap both of the above areas, emphasizing analytical methods to determining if a steroid is present in a mixture and determining its quantity.